fix: connection status indicator stuck at idle after component remount

[Copilot]

After extended usage, the connection indicator would permanently show idle despite the WebSocket remaining fully functional. Root cause was a window-singleton behaviour in @apollo/client-react-streaming.

Root Cause

ApolloNextAppProvider stores the Apollo Client (and its embedded graphql-ws client) as window[Symbol.for('ApolloClientSingleton')] ??= makeClient() — called once per browser session. On any ApolloClientProvider remount (locale change, error-boundary recovery, etc.), the new component instance starts with fresh useState('idle'), but the graphql-ws on:{} handlers still hold a closure over the first mount's setState. React silently drops setState calls on unmounted components, so the new instance's state is never updated — stuck at 'idle' forever while subscriptions continue working normally.

Changes

• Module-level forwarding callbacks (wsConnectionStateCallback, wsErrorCallback): graphql-ws event handlers now call through mutable module-level refs instead of directly closing over a per-instance setState.

• useEffect (empty deps) re-wires on every mount: points the module-level callbacks at the current component's setState; resets to no-ops on unmount so stale events don't touch an unmounted component.

• useState lazy initialisers read lastKnownConnectionState / lastKnownError (updated before each callback invocation) so a remounting component immediately reflects the correct state without waiting for the next WS event.

• globalWsClient + module-level wsIsResettingRef: ensures resetConnection() and the closed-event guard work correctly after a remount where the per-instance React refs are null.

// Before — captured setState_1 from first mount; dead after remount
on: { connected: () => setConnectionState('connected') }

// After — always dispatches to the currently mounted component
on: { connected: () => wsConnectionStateCallback('connected') }
// ...
useEffect(() => {
  wsConnectionStateCallback = (s) => setState(s); // re-wired on every mount
  return () => { wsConnectionStateCallback = () => {}; };
}, []);

Type of change

• Bug fix (non-breaking change which fixes an issue)

Screenshots

No UI changes — only the connection indicator's correctness is affected.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• My changes generate no new warnings